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Geometric phases for mixed states in interferometry

Sjoqvist, E and Pati, A K and Ekert, A and Anandan, J S and Ericsson, M and Oi, D K L and Vedral, V (2000) Geometric phases for mixed states in interferometry. Physical Review Letters, 85 (14). pp. 2845-2849. ISSN 0031-9007

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Abstract

We provide a physical prescription based on interferometry for introducing the total phase of a mixed state undergoing unitary evolution, which has been an elusive concept in the past. We define the parallel transport condition that provides a connection form for obtaining the geometric phase for mixed states. The expression for the geometric phase for mixed state reduces to well known formulas in the pure state case when a system undergoes noncyclic and unitary quantum evolution.